Catalysis Science & Technology

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May 25, 2017 - Bhatt, O. S. Nayal, S. Sharma, V. Kumar, M. S. Thakur, N. Kumar, R. Bal, B. Singh ... Vinod Bhatt,a,b,Â¥ Onkar S. Nayal, a,b Sushila Sharma,a,b Vishal Kumar,c ..... and Dr. S. C. Yadav for TEM analysis and insightful discussions.

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This article can be cited before page numbers have been issued, to do this please use: M. Kumar, V. Bhatt, O. S. Nayal, S. Sharma, V. Kumar, M. S. Thakur, N. Kumar, R. Bal, B. Singh and U. Sharma, Catal. Sci. Technol., 2017, DOI: 10.1039/C7CY00832E. Volume 6 Number 1 7 January 2016 Pages 1–308

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ISSN 2044-4753

PAPER Qingzhu Zhang et al. Catalytic mechanism of C–F bond cleavage: insights from QM/MM analysis of fluoroacetate dehalogenase

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CuI nanoparticles as a recyclable heterogeneous catalyst for C-N bond formation reactions Received 00th January 20xx, Accepted 00th January 20xx DOI: 10.1039/x0xx00000x www.rsc.org/

Manoranjan Kumar,a,b,¥ Vinod Bhatt,a,b,¥ Onkar S. Nayal, a,b Sushila Sharma,a,b Vishal Kumar,c Maheshwar S. Thakur,a,b Neeraj Kumar,† Rajaram Bal,*d Bikram Singh*a,b and Upendra Sharma*a,b Herein, copper iodide nanoparticles (NPs) are first time reported for the reductive amination of carbonyl compounds. The generated NPs were characterized by TEM, EDX, XRD and XPS analysis. The XRD pattern, XPS, and EDX analysis confirmed that the resulted NPs were of CuI instead of Cu. The TEM image of CuI exhibited the monodispersed spherical NPs size in the range of 4±2 nm. These generated NPs can be used as versatile heterogenous catalysts for important organic transformations. As a proof of concept, CuI NPs were successfully applied as a heterogeneous catalyst for the synthesis of secondary amines, amide and triazole. CuI NPs can be easily recovered and recycled up to six times.

Introduction Nowadays nanocatalysts are very popular in chemical industries, energy related applications and environmental remediation’s. The catalytic systems based on nanoparticles (NPs), are most promising candidates due to their broad spectrum of characteristics which forms the bridge over the heterogeneous and homogeneous catalysts.1 The recyclability and recovery offers heterogeneous characteristics whereas low catalytic loading and selectivity offers homogeneous characteristics of NPs.1 In addition, small dimension and large surface area of NPs, revealed high catalytic activity under mild conditions. Amino compounds are ubiquitous in natural products, synthetic intermediates and pharmaceutical agents.2 Therefore, efficient and economic synthesis of amines is a very active field in medicinal chemistry and modern organic synthesis. The introduction of amine functionality into organic framework is generally achieved by C-N bond formation strategies. Although, various methods for the synthesis of substituted amines viz. alkylation of amines, reduction of nitriles and Buchwald-Hartwig amination are known,3 the a. Natural

Product Chemistry and Process Development Department, CSIR-Institute of Himalayan Bioresource Technology Palampur, Himachal Pradesh 176 061, India. b. Academy of Scientific and Innovative Research, Anusandhan Bhawan, 2 Rafi Marg, New Delhi-110001, India. c. State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Weijin Road 300 071, Tianjin, China. d. Refining Technology Division, CSIR-Indian Institute of Petrolium, Dehradun, 248005. ¥ These authors contributed equally †Author deceased. *E-mail: [email protected], [email protected] (US); [email protected] (RRB); [email protected] (BS) Electronic Supplementary DOI: 10.1039/x0xx00000x

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direct reductive amination of carbonyl compound is one of the most convenient and efficient method to facilitate the synthesis of complex amines. Previous approaches have been focused on the use of precious metal based catalysts such as Au, Pd, Pt, Rh, Ir and Ru for this transformation.4 However, limited availability, high cost and toxicity of these metal based catalyst, turned researchers towards the environment friendly and easily available bio-relevant metal based catalysts such as Zn,5 Fe,6 and Co7. However, high catalyst loading, longer reaction time and non-ecofriendly solvent limits the scope of these methods. Hence a simple approach with minimum catalyst loading to control the quantity of heavy metal waste at the end of reactions is highly desired. In this context, the catalytic system based on NPs, played a vital role. Previously, nanocatalyst viz Pd8 and Ni9 were reported for the synthesis of amines via C-N bond formation strategies. The separate step for nanometal preparation, high cost of palladium salts and toxicity of nickel limit their scope. These limitations can be overcome by the use of less expensive and bio-relevant CuI nanoparticles (NPs). Herein, we disclose a new and simple method for the synthesis of CuI NPs and successfully applied these NPs as heterogeneous catalyst for various C-N bond formation reactions to synthesize secondary amines, amide and substituted triazole. This is first report on CuI catalyzed direct reductive amination of carbonyl compounds.

Result and discussions In continuation of our interest on reductive amination,10 herein we disclosed a new method to prepare CuI NPs using phenylsilane in ethanol without the use of additional stabilizing agents. Furthermore, CuI NPs have been utilized as heterogeneous catalyst for reductive amination of carbonyl compound to synthesize secondary amine. Recently, Beller and co-workers reported the first successful copper(II) catalyzed

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Catalysis Science & Technology Accepted Manuscript

DOI: 10.1039/C7CY00832E

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reductive amination of ketone using molecular hydrogen as reducing agent but non recyclability of the catalyst limit the scope of this method.11 To identify the best reaction conditions, the direct reductive amination of benzaldehyde with aniline was chosen as model reaction and subjected to a series of different copper catalysts, reducing agents and solvents under varying temperature conditions (Table 1). Table 1 Optimization of reaction conditions for reductive amination.a CHO

NH2

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+

Catalyst (3 mol%) Reducing agents (1.5 equiv.)

N H

solvent, 80 oC 4h

Entry

Catalyst

Reductant

Solvent

Yield [%]b

1

CuI

PhSiH3

EtOH

92c

2

CuSO4

PhSiH3

EtOH